We have demonstrated the indestructibility of matter in modern times by experimental methods. The mediaeval schoolmen reached similar conclusions, however, by strict reasoning from the premises of observation that they had in the olden times. We may be apt to think that they knew very little about nature and the details of physical science, but that will be only because we do not {112} know their great books. Albertus Magnus is a typical example of a renowned teacher of the thirteenth century who was, however, at the same time a highly respected member of his order, holding important official positions in it and thoroughly honored and respected by his ecclesiastical superiors so that he was made a bishop, yet writing volumes of observation with regard to nearly every phase of physical science. A list of his books reads like a section of a catalogue of a library of physical science. I have told the story of his career in the second series of "Catholic Churchmen in Science," but the names of his volumes are sufficient to show what sort of work he was doing. He has volumes on chemistry, botany, on physics, on cosmography, on animal locomotion, on respiration, on generation and corruption, on age and death and life, on phases of psychology, the soul, sense and sensation, memory, sleep, the intellect and many another subject. Those who think that there was no attention paid to science in the Middle Ages must know nothing at all of Albertus Magnus' work. Above all, those who talk thus are entirely ignorant of all that Roger Bacon did. Roger Bacon himself was a student of the University of Paris. He was a professor there. He corresponded with the scientists of Europe quite as frequently or at least as significantly as professors of the modern time do with each other. Students submitted their discoveries to him. We {113} have Peregrinus' letter to him with regard to magnetism and electricity and know of others. We have his own books, in which he treats not only the scientific problems, but inventions and applied science of all kinds. At the present time his interest in aeronautics has a special appeal to us. He was sure that men would sometime make a successful airship. He even thought that he could make one himself, but his experiments proved unsuccessful. His theory of it was very interesting. In his work "De Secretis Artis et Naturae Operibus" he writes that a machine could be constructed in which a man sitting in the centre might move wings by means of a crank and thus, quite after the fashion of birds, fly through the air. It was he who wrote that the time would come when carriages would move along the roads without men or horses to pull them. At the moment he was experimenting with gunpowder. He realized, therefore, that sometime men would harness explosives and use them for motor purposes. That is, of course, just what we are doing with gasolene.